DESCRIPTION: The proposed experiments are designed to continue the PI's studies of the NimA protein kinase of the filamentous fungus, Aspergillus nidulans. Previous work, almost entirely from the PI's laboratory, has demonstrated that NimA is required for passage through mitosis and is regulated by complex mechanisms involving phosphorylation and degradation. There is some evidence for NimA homologues in other eukaryotes, suggesting that this kinase is generally important in the control of eukaryotic mitosis. In the present application, the PI proposes an extensive series of experiments that will address several aspects of NimA function. There are five specific aims: (1) Genetic and biochemical approaches will be used to identify proteins that interact with NimA. Significant progress has already been made toward the characterization of SonA, an extragenic suppressor of a NimA mutation. (2) The PI proposes to study the role of ubiquitination in the mitotic degradation of NimA. (3) Phosphorylation sites on NimA will be mapped and mutated to determine their role in NimA regulation. (4) The role of NimA in the S phase checkpoint will be explored. Preliminary experiments suggest that inhibition of DNA synthesis may block mitotic entry through inhibition of NimA. The proposed experiments will characterize the control of NimA gene expression by Cdc2 and the control of NimA phosphorylation by BimE, a protein also implicated in NimA control during S phase arrest. (5) Experiments are proposed to further define the precise function of NimA in mitosis, with an emphasis on its role in spindle asembly.